A great deaf is known about the afferent and efferent pathways responsible for mediating the Hering-Breuer Inflation reflex, but very little is known about the central nervous system pathways that are involved in this reflex arc. The influence of the Hering-Breuer Inflation reflex on respiratory rhythmogenesis and cardiovascular control has been studied extensively, while the influence of this reflex on airway tone has largely been ignored. The proposed studies are designed to elucidate the central pathways mediating the airway response to the Hering-Breuer Inflation reflex. Three central pathways, which have been documented as being significant in central respiratory control, will be examined during the course of the proposed studies. These pathways will be studied using g chemical stimulation of neuronal cell bodies to determine if the activation of potential relay sites reduces airway tone in a manner which mimics the activation of the Hering-Breuer reflex. Synaptic transmission will be blocked transiently at potential relay sites to determine if this maneuver attenuates or prevents the reflex airway response to lung inflation. Anatomical tracers will be used to confirm the participation of these potential relay sites in the Hering-Breuer reflex arc. Extracellular single-cell recording will be used in conjunction with antidromic stimulation of vagal branches that innervate the airway to permit the characterization of the spontaneous discharge pattern(s) of vagal tracheomotor and bronchomotor preganglionic neurons. These recordings will also permit the characterization of discharge response of these vagal preganglionic neurons to lung inflation before and during the blockade of synaptic transmission at the potential relay sites.